Maturation of human blood neutrophils is associated with development of specific antigens which have been shown to be present only on these cells. These antigens are controlled by several independent genetic loci, and their in vivo reactions with the corresponding antibodies have been shown to have important clinical implications. These include neonatal neutropenia due to fetal-maternal incompatibility, autoimmune neutropenia of infancy and adults, pulmonary, and most likely, febrile transfusion reactions. It is the purpose of this investigation to broaden our present knowledge on the pathophysiology of neutrophil antigens, and then by using the neutrophil model, explore the possibility that similar organ-specific alloantigens with similar biological implications, exist in other tissues. The study would include: 1. Search for new neutrophil-specific antigens, and procurement of new typing reagents by a) investigation of new cases of neonatal neutropenia, and b) production of xenogeneic antisera using purified antigens for immunization. 2. Development of new techniques for neutrophil antibody detection including manual and instrumented passive hemagglutination tests, and quantitative complement fixation, antiglobulin consumption, and fluorescent microscopy. 3. Study of various immunological forms of neutropenia, and determination of their relation to neutrophil antigens. 4. Solubilization and chemical characterization of those antigens prepared by cell extraction, and found in urine and heavy density serum lipoproteins. 5. Determination of the importance of individual neutrophil antigens in blood transfusion reaction, and bone marrow transplantation. 6. Demonstration of similar allospecificities in other organs, and evaluation of their implications in organ transplantation and autoimmune disease of the respective organs.